very few Dell laptops are upgradeable,as their thermal/power considerations at most will allow perhaps a 100 Mhz faster CPU, which would be unnoticeable anyway, assuming the cpu is not soldered in...
Best to look for a newer laptop, with an SSD, and at least 8 gb of RAM.... (Never buy a Win 10 laptop with only 4 gb of RAM which Dell loves to sell for $329 or so)